With the rising popularity of mobile terminals such as smartphones, there has been an increase in the number of base stations that connect the mobile terminals to a wireless communication network. Among the base stations, small cells have been increasingly provided in order to make up for local bandwidth shortages of macro-cell base stations that cover macro cells, so that the small cells cover small cells provided to overlap the macro cells (for example, see Japanese Laid-open Patent Publication No. 2011-103570).
Meanwhile, in some cases, a passive optical network (PON) with low installation costs of optical fibers is used as a mobile backhaul network that connects a large number of base stations to an upper-level accommodating station, (for example, see International Publication Pamphlet No. WO2014/103804). For example, IEEE802.3ah of the Institute of Electrical and Electrics Engineers, Inc. defines a technique for a gigabit Ethernet (GE)-PON (Ethernet is a trademark, and the same applies below) of 1 or more Gbps in conformity with the Ethernet.
The PON is a star-type access optical network in which an optical line termination is connected to multiple optical network units via an optical coupler that splits light. The optical line termination is abbreviated as OLT, and the optical network unit is abbreviated as ONU. Employing the PON as the mobile backhaul network may obtain not only an advantage of reduction in the installation costs of optical fibers, but also an advantage in that one OLT may transmit the traffics of multiple base stations.
Moreover, for example, as disclosed in Japanese Laid-open Patent Publication No. 2011-103570 and International Publication Pamphlet No. WO2014/103804, known is a technique in which part of the operations of the base stations and the ONUs is suspended depending on the traffic conditions to reduce the power consumption.
A continuous increase in the number of base stations may result, in the future, in a shortage of the PON that may be utilized as a mobile backhaul network. In one possible way to solve the shortage of the PON, for example, communication channels of the base station may be accommodated within a PON that accommodates therein communication channels (for example, access channels to the Internet) provided in a house of a subscriber, such as an office building.
However, in this case, communication channels of different usage purposes are present in one PON, and multiple ONUs share the bandwidth within the PON, so that it is difficult for an upper-level accommodating station of the base station to know a traffic condition within the PON in the base station. Accordingly, in order to reduce the power consumption, for example, the accommodating station may perform sleep control of the base station which is currently connected to a small number of mobile terminals, but, the sleep control may be inappropriate from the view point of the traffic condition.
The present application was made in view of the abovementioned problems, and aims to provide an optical line termination, a communication system, and a communication control method that appropriately reduce the power consumption.